FIELD OF THE INVENTION
The present invention relates to an apparatus for manufacturing semiconductors which have become more sensitive year by year. Specifically, the present invention relates to a vibration-proof mechanism of a reduction projection aligner (stepper) having a stage for a step and repeat, or step and scan operation installed therein.
Hitherto, an apparatus of the above type has used a vibration insulation system, as shown in FIG. 4, in order to reduce the influence of floor vibrations where the apparatus is installed. In this system, as floor vibration transmission prevention means, vibrations along the Z axis are prevented by means of an air spring 2 which is vertically suspended by a suspension member 4 so that horizontal vibrations are prevented based on the principle of a pendulum. The inside of an outer suspension casing 6 is filled with viscous fluid 5 in order to improve horizontal damping characteristics. The damping using viscosity resistance is performed by the bottom surface of a suspender which is equivalent to a pendulum and the surface of a container. The rigidity of the air spring along the Z axis can be reduced in this system, and low rigidity of a suspension member can also be assumed horizontally. Furthermore, by using a long suspension member, the characteristic horizontal vibration frequency can also be suppressed to quite a low level. Therefore, this method has been put into practical application in apparatuses as a very effective method for attenuating floor vibrations.
As shown in FIG. 5, a system has recently been developed in which a sensor 22 for detecting vibrations of the apparatus and an active control apparatus 21 for regulating the amplitude of the vibrations is incorporated into a conventional vibration insulation system. However, problems remain to be solved, for example, the apparatus is large, and costs are quite high.
Systems of the above type are generally designed with a view to inhibiting floor vibrations from being transmitted to the apparatus. Usually, such systems are not effective for controlling vibrations generated by the apparatus. That is, the transmission function of a vibration transmission ratio (smaller than 1) for preventing vibrations from being transmitted to the apparatus is in a reverse relation to that of the vibration transmission ratio (smaller than 1) for controlling vibrations generated by the apparatus in frequency regions. Therefore, it may be considered that the reason why such systems are not effective is that conflicting characteristics are needed in a conventional stepper using the vibration insulation system of the above type. Vibration insulation characteristics with respect to floor vibrations have been sacrificed to some extent, and a vibration control effect for controlling vibrations generated by the apparatus is added thereto. However, as semiconductor devices have become more sensitive in recent years, these very small residue vibrations have reached an unacceptable level.
Therefore, since alignment and exposure are performed after residual vibrations are attenuated naturally, the productivity of the apparatus decreases considerably. This is extremely inconvenient. A semiconductor exposure apparatus is disposed on a second or higher floors rather than on the first floor in some recent semiconductor manufacturing factories because it is difficult to secure sites. In some cases, the level of floor vibration is high. In these circumstances, it is necessary to develop a vibration insulation system capable of efficiently and quickly insulating floor vibrations and attenuating vibrations generated by the apparatus.